Electronic stability control (ESC, also referred to as ESP or DSC) is required by law on passenger cars/SUVs to stabilize the cornering behavior and reduce accidents involving loss of control. ESC for passenger cars is typically an automated brake system combined with engine power reduction in which the brake is individually controlled for each wheel in order to influence the yawing and lateral motion of vehicle.
For motorcycles, motorcycles can become unstable when operating at high speeds and at high cornering levels. For example, they can exhibit an oscillation at the rear wheel commonly known as “weave.” ESC for motorcycles (also referred to as ASC/MSC) have appeared on the market. Most of these known stability control systems operate to control only the throttle reduction and front/rear brake distribution with an anti-lock braking system (ABS) in which the brakes are still applied by a rider. Automatically controlling the brakes on a motorcycle without rider intention is risky, with the possible consequence of falling over or in other words, capsizing.
It is an object of the present invention to provide an improved stability control system and method which overcomes disadvantages associated with the prior art.
More particularly, the system and method of the invention presents a controller method for actively applying the brakes on a motorcycle or other similar vehicle having two or more wheels that can improve stability in low-friction conditions without losing safety.
It is well known that motorcycles possess the vibration modes of weave, wobble and chatter. Weave is typically a lightly damped vibration around 2.5-4 Hz that becomes unstable at high speed (>180 km/h) on high-friction surfaces. On low-friction conditions, the weave becomes unstable at mid-range speed, especially during steady cornering. The ESC system and method of the present invention predicts a yaw rate, and applies both front and rear brakes when an oscillation occurs, and only in the part of the vibration where the actual yaw rate is less than the predicted rate. The controller is designed using MATLAB/Simulink software using a high-fidelity, multibody, motorcycle-dynamics model, such as BikeSim®, which is sold by the assignee of the present invention. This software provides a time-domain simulation environment that is used to evaluate the performance of the motorcycle in extreme nonlinear conditions. In addition, a linearized controller and motorcycle model (BikeSim-Linear) are used to examine the stabilities for variations in speed on root locus.
In one example, the controller can be used to predict the yaw rate overlaid with the yaw rate from a fully detailed multibody simulation along with front and rear brake pressures for a 304.8-m constant-radius curve, 50% road friction, ridden with a speed of 145 km/h, and requiring lean of about 30 deg. The controller predicts the yaw rate based on the vehicle's speeds (longitudinal and lateral), roll angle, and steer. The internal controller model includes only a few vehicle properties, such as weight, CG location, wheelbase, etc. As may be shown in plots, the controller preferably applies the brakes only when the actual yaw rate (which would be measured directly in a physical system) is less than the predicted yaw rate. In one scenario, a motorcycle without the inventive ESC falls down after the weave motion builds to an unstable conclusion, while a motorcycle using the system of the present invention would remain upright since the weave mode is stabilized by the inventive ESC in an entire speed range, although the wobble might become a little unstable under some conditions.
The invention described here utilizes a high-fidelity computer simulation model of a 2- or 3-wheel motorcycle or similar vehicle to predict operating states such as yaw rate, lateral acceleration and roll angle for a stable motorcycle at a given speed and steer angle. For purposes of this disclosure, the term motorcycle is used for explanatory purposes, although it will be understood that the invention and its reference to motorcycle would also encompass other two- or three-wheeled vehicles. According to the invention, the operating state of a physical motorcycle can be measured and compared to that of the model at every instant in time to determine if the operating state of the physical motorcycle differs from that of the simulation model in such a way as to indicate loss of stability. The nature of that difference can then be used to intervene in the operation of the motorcycle independent of driver actions by application of brakes, modulating the engine torque or applying torques to urge the steering system in a corrective direction. Thus by comparing the physical response of the motorcycle to that of the computer model in an on-board controller these interventions can be applied at a time and intensity to stabilize the motorcycle and prevent a loss of control.
Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience and reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.